Study On Oil Displacement Effect Of Alkali-free Binary Compound System In D Oilfield

The average reservoir permeability of D oilfield is about 330×10-3 m,the burial depth of the reservoir is about 900 m,and the viscosity of formation oil is 4.9MPa.s.At present,the oilfield has entered the development stage of ultra-high water cut,but the degree of formation oil recovery is low,only 33.05%,so it is difficult to continue water flooding and the economic benefit is poor.Due to the low recovery degree of single oil displacement,there is great potential for development.Polymer flooding mainly increases the oil washing efficiency by increasing the viscosity of the displacement phase,while surfactant can exert the interfacial activity and change the wettability to improve the oil washing efficiency.Therefore,in order to realize efficient and sustainable development of D Oilfield,this paper studies the displacement effect of polymer/surface binary composite system for D Oilfield.In this paper,under the guidance of polymer flooding and surfactant flooding technology theory,through the analysis of modern equipment and indoor physical simulation experiments,the polymer and surfactant were initially optimized and screened.Then,the solution properties of the binary composite system were studied to analyze the effects of surfactants,stabilization time,adsorption and salinity on interfacial tension.The effects of surfactant on the viscosity,water separation rate,emulsion viscosity and particle size of the composite system were also studied.Finally,the optimum polymer concentration,surfactant and concentration binary composite system were optimized by indoor displacement physical simulation experiment.The experimental results show that:(1)The higher the polymer concentration and molecular weight,the stronger the viscosity increase,the smaller the viscosity retention rate after shear,and the higher the resistance coefficient and residual resistance coefficient.Salt-resistant polymer solution after shear viscosity loss is greater,but salt-resistant polymer viscosity has a strong shear recovery,salt-resistant polymer molecules formed a special network structure,making it difficult to inject,easy to plug.The surfactants are S1#,S3# and S4# according to the oil-water interfacial tension.(2)Surfactant and adsorption have the greatest influence on the interfacial tension of the composite system,while salinity and time have little influence on the interfacial tension.The interfacial tension adsorption loss of S3# composite system is the largest,and the interfacial tension resistance of S1# and S4# composite systems is stronger.(3)S1# active agent and polymer form aggregates,resulting in a certain viscosifying effect,the viscosity is greater than that of S4# composite system.(4)The emulsion viscosity of S4# system is greater than that of S1# system,and the median particle size of the emulsion formed by the stability of the emulsion and the space resistance of the emulsion is greater than that of S4# system.(5)The higher the concentration of polymer and surfactant,the greater the chemical flooding recovery;The viscosity and particle size of oil-water emulsion have dual effects on recovery efficiency.Finally,the optimal displacement system is 0.3%S4#+1400mg/LP2 for the reservoir with 400×10-3μm2 permeability and 0.25%S1#+1000mg/LP2 for the reservoir with 200×10-3μm2 permeability through the displacement experiment,and the indoor recovery efficiency is the best.25.38% and 18.45% respectively.